Production of iodine from molten lithium iodide



United States Patent 3,169,830 PRODUCTION OF IODINE FRGM MOLTEN LITHIUM IODIDE Jennings B. Du Bois, 51"., Pasadena, Tex., assignor to amount of reaction has been efiected; e.g. more than about 5% of the lithium iodide, the amount of lithium paraperiodate, which is an insoluble solid, is sufiicient to represent a material reduction in efliciency of utilization 'fy the Ne York NY a oration f 5 of the oxygen for liberating dl1'l6 and to mod j g gi w p physical character of the system so as to change 1ts flow No Drawing. Filed Oct. 18, 1963, Ser. No. 317,128 characteristics and tend to plug the reactor. It has been 5 Claims. (Cl. 23-216) found further thatwhen the oxidation is carried out in the presence of sufficientwater to react with lithium oxide This invention relates 9 P F F f 10 formed by reaction of oxygen with lithium iodide, the production of elemental or free iodine from lithium odide. amount of lithium paraperiodate f d is Substantially More particularly, it relates to productlon of lodine by reduced I. v oxygenative oxidation t p p a a elevated A better understanding of the invention will be Obttimpelatule at wilich the hthlum lodlde 1s m a molten tained by consideration of the results of a series of runs, state. 4 15 in some of which dry oxygen was passed into molten It has recently b p p (Neger, US 3,980,435, lithium iodide at 566 c. 1050" F.), and in some of iss d March 5, 1963) to f y fi ifi q which a mixture of oxygen and steam in a 1:1 mol ratio Pounds y a Process iIW1V1I1g3 lodlnatlve dtfhydro" was passed into molten lithium iodide under similar congenation 0f the Organic c0II1l10111 1d PY l'eacflon Wlth l ditions. The results of the runs with dry oxygen are mental iodine in a molten metal iodide envlronment with given i Table 1 hil the results with the r f i Th6 Production of dehydflogel'lated Compound n tures of oxygen and steam are given in Table 2. i

TABLE 1 Dry oxygen results Orig. wt of L11 (g:) 13.937 13.857 14.015 13. 992 14.135 :14. 051 13.893 18.949 Wt. oiresidue (g) 11.331 9.602 9.037 8.613 7.895 7.850 7.662 Percent Wt. 111 residue:

1 Not determined. 2 Based on Lil converted.

hydrogen iodide, (2) immediate reaction of the produced TA L 2 hydrogen iodide with the corresponding metal oxide or hydroxide in the dehydrogenation zone to produce the Oxygen/steam mixture results metal iodide, and (3) regenerating elemental iodine from 40 i I V 9 t meal iodide. ether m the dehydeeeeeon or asuirisaair is; a2 a; as: in a separate oxidation zone,- by reaction with elemental PercentWt. in residue or free oxygen under conditions such that the metal iodide E k- 2;; 33-2 is in a molten state. The use of lithium iodide as the Li5I0i' 'II II 0:6 115 419 9:7 9:3 metal iodide has been disclosed as a particul ly usef alli s? I &3? 1 9 35333 3:27 1 5 metal iodide for the process. However, it has been found PercentWt. M12 92,4 89.2 90. 5 88. 6 90. 4

that when lithium iodide is utilized in this dehydrogenation process, the efliciency of the oxygenative oxidation of the lithium iodide to elemental iodine is often lower than desirable and that the physical condition of the molten mass changes with time and insoluble, inorganic material is formed with the resultant tendency to plug equipment, and thereby impair operation of the process.

It is a principal object of this invention to improve the oxygenative oxidation of lithium iodide in the molten state to produce free iodine and at the same time to minimize the production of insoluble inorganic material in the system.

Now, in accordance with the present invention, it has been found that the efiiciency of oxygen utilization in the oxidation of lithium iodide to produce free iodine is en hanced, and the formation of undesirable, insoluble inorganic material in the system is substantially reduced by effecting the high temperature reaction of the oxygen with the lithium iodide in the presence of approximately a stoichiometric amount, with respect to the oxygen, of water, or an excess thereof, while maintaining the system at a temperature of from about 400 C. to 650 C.

It has been found that when oxygen is reacted with molten lithium iodide in the absence of water, lithium paraperiodate is formed and that after a substantial 1 Based on Lil converted.

there are upper and lower limits to this percentage. The

upper limit is at'94.8% and corresponds to the percentage weight of iodine in lithium iodide, and the lower limit is at four-fifths this value (75.9%) and corresponds to total lithium paraperiodate formation. In the latter case, complete conversion of lithium iodide to lithium paraperiodate results in the retention of one-fifth of the available iodine in the residue.

As already indicated, as far as the operation of the iodinative dehydrogenation process is concerned, several undesirable consequences result. The maximum yield of iodine is not obtained since some of it, along with some of the feed oxygen is retained as lithium paraperiodate, and further, the lithium paraperiodate is solid at reaction temperature and tends to plug the reactor.

Fortunately, as shown by the results in Table 2, the

foregoing undesirable consequences are. alleviated substantially by passing steam into the oxidation zone along with the Oxygen. The results in Table 2 show that the amount oflithium parape'riodate formed is reduced substantially and correspondinglymore free'iodine is produced. Furthermore, the" major constituent of the inorganic residue," besides lithium iodide; is'lithium hydroxide which melts at 463 C. (865 F.) and whichis completely miscible with lithium iodide in all proportions at 'atein perature above its melting point; they arei'rnis'cible above aqueous solution. The reaction conditions and reaction zone, of course, will be selected so as to insure the 7 presence of the essential reactants, oxygen, steam'and lithium iodide, with the lithium iodide being in a molten state'at a temperature offrfonf-460-650 C. The use of an excess of water is 'advastageeus'sqaswin ers rapid and complete reaction of lithium oxide as formed to 400 C. in proportions from about mol percent lithium p hydroxide to about 90' mol percentjlithium' hydroxide;

When used in connection vvith'the"iodinative aeh 'dn;

genation, elgias disclosed in US. 3,080,4 35,a nd wherein: p the molten'lithium iodide is separately'oxidi'ied'by 'free oxygen to liberate free iodine to be used in a separate dehydrogenation zone,'the"pres'ent invention is particularthe ilithiurnf iodide in the molten litliiurn "iodide compost tion withdrawn from the dehydrogenation" zone; that is, an amount of oxygen 'isutili'zed to] effect an oxidation of 5-1. 75% of thelithium iodide; Ofcourse, if desired, essenlithium hydroxide; from about 1 to 5 stoi'chiometric'proportions being adequate. Larger proportions a be used without adverse effects except for the uselessrdilution of the liberated iodine.

Thus, the present invention'proyides a process for'the reaction of oxygen with lithium iodide ina molten system 'which consists essentially of lithium iodide in-a single 1 phase mixture with any proportion oflithium hydroxide; at a temperaturerfrom' about 400 Cito 650 C. in thepresence of an amount of Water corresponding to the tially compl'et'e' oxidationof the iodide may be carried I out. 1

Investigation seems to indicate that two reactions are involved in the formation ofthe'undesirable lithium" paraperiodate. The first reaction, which is'are'latively fast reaction within the high temperature range indicated hereinbefore MOO-650 C.), is the reaction of lithium iodideandoxygnftofform lithium oxide and iodine, in

' accordance with the-equation The second reaction, amuch faster reaction," is the reactionf'of the formed lithium oxide with lithium iodide and;

oxygen to 'form lithiuni paraperiodate, in accordanc with the equation:

' The addition of excess Water (steam) to the oxidation system minimizes the formation of lithium paraperiodate. v

This is accomplished by obstructing the second of the foregoing reactions, possibly; by reaction with", the formed lithium oxide to yield lithium hydroxide, since-thesteanidoes not react with the lithium paraperiodate.

As already indicated in the series of runs, the results of which are given in Table 2, the Water may be introduced as steam admixed with the oxygen. However, as will be readily understood by those skilled in this art; the water may be introduced by other means. For example, it may i be introduced to the oxidation z'one 'ad'niixed'witli a portion" of lithiiiin' iodide" and/ or lithium hydroxide as an lithium oxide formed by the reaction of the oxygen with; lithium iodide, or an excess of water, witha substantial reduction in the production of lithium paraperiodate and an enhancementinj-the utilization'oftheoxygen to pro duce free iodine; r

The invention claimed is:

1. A process for the production offr'ee iodine tromlithium iodide while minimizing the formation of lithium paraperiodate by reacting. lithium iodide in molten state at a temperature of from 400 to 650 C. with elemental oxygen in amount sufficient to oxidize from. about 5% to V of the lithium iodide and at least about a stoichiometric amount of steam based on the oxygen reacted. 2. Apro'cess 'in accordance with claim 1 wherein the temperature isabout 550 C. r

' 3.v A process in accordance'with claim 1 wherein the llithium iodideis present as an essentially single liquid ipliase with lithium hydroxide.

Refetn'ce Cites w Exa ine; 1

UNITED STATES/PATENTS 1,324,761 12/19 cart'r 235 213; 1329;457 2/20 Carter 23am 3,044,862 *7/62 5 Paul i 23*21s x OTHER REFERENCES Becket aL: SerialNo; 292,742, published July 13,1943. 7 p MAURrcE A. BRrNnts'i, Primary Examiner; 7 

1. A PROCESS FOR THE PRODUCTION OF FREE IODINE FROM LITHIUM IODIDE WHILE MINIMIZING THE FORMATION OF LITHIUM PARAPERIODATE BY REACTING LITHIUM IODIDE IN MOLTEN STATE AT A TEMPERATURE OF FROM 400 TO 650*C. WITH ELEMENTAL OXYGEN IN AMOUNT SUFFICIENT TO OXIDIZE FROM ABOUT 5% TO 75% OF THE LITHIUM IODIDE AND AT ELAST ABOUT A STOICHIOMETRIC AMOUNT OF STEAM BASED OM THE OXYGEN REACTED. 